Hepatitis A virus (HAV) is a morphologically, biochemically and immunologically distinct agent which produces infectious hepatitis A in humans after an incubation period of approximately 2 to 6 weeks. Hepatitis A is a liver disease which, although not commonly fatal, can induce long periods of debilitating illness. An estimated 1.4 million cases of hepatitis A are reported annually worldwide. The disease is commonly spread by direct contact with an infected individual or by HAV-contaminated drinking water and/or food.
HAV has been characterized as a picornavirus belonging to the enterovirus group. Like other picornaviruses, HAV is 27 nm in diameter and contains a single-stranded, positive-strand infectious RNA genome coding for a single polyprotein which is subsequently processed into structural and nonstructural proteins. Four major capsid polypeptides have been described with molecular weights of 32,000 to 33,000 (VP1), 26,000 to 29,000 (VP2), 22,000 to 27,000 (VP3) and 10,000 to 14,00 (VP4). There appears to be only one serotype and significant antigenic variation has not been recognized among different HAV strains.
HAV infection is typically diagnosed by the detection of IgM or IgG antibodies to the capsid proteins. Prior art, recombinant proteins or synthetic peptides have not successfully been used as alternate sources of antigen in an enzyme immunoassay (EIA) format for the detection of anti-HAV, a serum marker of infection, because of poor antigenic reactivity due to the strictly conformational nature of HAV antigenic epitopes. For more than 15 years, the only available source of immunoreactive proteins was from HAV grown in cell culture. In fact, inactivated cell culture derived HAV is used by all commercial companies who manufacture anti-HAV tests. Unfortunately, HAV is made in very small quantities in cell culture, has a limited animal host range, and is difficult to purify from infected cell cultures and animal tissues. In addition to the inconvenience and cost associated with the production, purification and standardization of cell culture derived HAV antigen, current commercially available assays are unable to discriminate between natural infections and vaccine induced immunity as emphasized in several publications (See, e.g., Jia, et al., J. Infect. Diseases 165:273-280 (1992); Robertson, et al., Vaccine 10(Supp. 1):106-109 (1992); and Robertson, et al., J. Med. Virol. 40:76-82 (1993)), because these tests utilize intact HAV and therefore will detect both kinds of immune responses.
As such, there remains a need in the art for synthetic peptides which can be used as alternate sources of antigen in an enzyme immunoassay (EIA) format for the detection of anti-HAV. In addition, there remains a need in the art for methods which can be used to discriminate between vaccine-induced immunity and natural HAV immunity. Quite surprisingly, the present invention remedies such needs.